In the Eterna City Pokémon Center, a lady in there gives you the Friendship Checker App for your Pokétch. By touching the Pokémon of your choice, hearts will show up. The bigger or more hearts, the happier your Pokémon is!
On the beach underneath Pastoria, in the house labeled 'Dr. Footprint'
or
In Hearthome, there is a building called 'Pokemon Fan Club.' In the back, there's a little girl who will tell you how much your Pokemon like you.
Its happiness must be high.
cleffa evolves into clefairy when its happiness is full, you can increase this by feeding it berries, giving it to the massage girl in veilstone city (Pokemon diamond, pearl, platinum), leveling it or giving it vitaminds. you can check its happiness in the Pokemon fan club in hearthome city (Pokemon dpp)
Pearl and Platinum
Buneary evolves by having happiness on max than you get a Loppuny!
In order for Buneary to evolve into Lopunny is that Buneary's happiness has to be 220.
get the Poke tech App Poke happyness
you can check a pokemons happiness in Diamond/pearl by the use of a poketch app, in previous games you could only know in the happiness was maxed by obtain a ribbon from a certain character depending on the game.
Pichu evolves by happiness.
Its happiness must be high.
It's on your Poketch.
There is no Action Replay code to max happiness in Pokémon Diamond. You can easily max a Pokemon's happiness by feeding it berries and vitamins as well as giving it a soothe ball.
cleffa evolves into clefairy when its happiness is full, you can increase this by feeding it berries, giving it to the massage girl in veilstone city (Pokemon diamond, pearl, platinum), leveling it or giving it vitaminds. you can check its happiness in the Pokemon fan club in hearthome city (Pokemon dpp)
You get it from a women on 1FL of the Pokemon Centre in Eterna City.
Pearl and Platinum
With the happiness checker you get in the Pokemon center in etera city.
You can check a Pokemon's happiness at a game's happiness checker. Where the person is located depends on the game you are playing.
It means thAt. That Pokemon is at maximum happiness and if youcan answer this , where can you find a happiny in any of the three Pokemon games ( platinum pearl or diamond )